1. Field of the Invention
The present invention relates to a dry etching method, and more particularly, to a method of reactive ion etching (RIE) of aluminum or aluminum alloy conductor lines (wiring pattern) of a semiconductor device.
2. Description of the Related Art
In the production of a semiconductor device (LSI etc.), dry etching methods are adopted because of their superiority to wet etching methods with regard to selectivity, fine pattern formability, controllability, cleanability, and the like. In particular, taking productivity and the anisotropic etching into consideration, a reactive ion etching system is widely used.
The density (integration degree) of semiconductor devices has been greatly increased, and the conductor lines of aluminum or aluminum alloy (hereinafter Al) are formed in finer patterns. Namely, the width of an Al conductor line is reduced and a distance between each the Al conductor line is also reduced. Where an Al layer is selectively etched (i.e., patterned) by an RIE method, usually a sidewall of an Al conductor line has an angle (slope angle) of approximately 90.degree. (vertical) to a groundwork surface. Then, when an insulating layer of PSG or the like is formed, in order to cover the Al conductor lines, the surface unevenness of the insulating layer becomes larger, which causes step coverage defects of upper conductor lines formed on the uneven surface, i.e., crack in the insulating layer at corners bounded by the sidewall and the groundwork surface, and voids in the insulating layer at the narrow space between the Al conductor lines. These defects shorten the lifetime of the semiconductor device. Accordingly, problems arise with regard to the insulating layer between conductor patterns. A solution to the problem was proposed in which a method of taperingly etching an Al layer for the Al conductor lines having sloped sidewalls was adopted.
Two conventional taper etching methods are most widely used, i.e., a proportion of an etch rate of the Al to that of a mask pattern resist (a selectivity of Al over resist) is decreased, so that the mask dimensions are gradually made smaller by etching, with the result that the sloped sidewalls of the Al conductor lines are formed (for example, cf. Japanese Examined Patent Publication (Kokoku) No. 61-59658), or a carbon-containing gas such as C.sub.2 H.sub.2 or CHCl.sub.3 generating a deposit on the Al sidewall is added to an etching gas, to form the sloped sidewalls, for example, cf. News review "Vacuum Magnetron RIE Apparatus Able to Dig Groove at High Speed and to Perform Taper Etching of Al", Nikkei Microdevice, February, 1987, pp. 148-149).
However, in the former taper etching method, since an Al layer for Al conductor lines has an uneven surface due to a groundwork uneven surface, the thickness of the mask pattern resist is not constant. Thus a thin portion of the resist is made smaller at a faster rate than that of a thick portion, so that an undesirable overetching of Al conductor lines covered with the thin portion occurs, and breakage of the Al conductor lines may occur. In the latter taper etching method, the deposit is formed on a chamber wall, electrodes and the like, and the deposit is then peeled off to form a contaminant. These problems prevent any improvement in the LSI production yield.
During the RIE of Al, the bombardment of active radicals and ions generated in a plasma and the exothermic reaction of chlorine (Cl) with aluminum, raise the temperature of a substrate (e.g., wafer). Accordingly, at a high rf power and/or a high etch rate, the substrate temperature becomes too high and chars the mask pattern resist, and an abnormal reaction occurs in the substrate. To prevent this charring and abnormal reaction, usually the substrate is placed on a water cooled stage and the RIE is performed while the substrate is cooled. Under these conditions, the contact between the substrate and the cooled stage is small, and therefore, a sufficient heat transfer is not carried out, with the result that the substrate temperature rises during the etching. When the substrate temperature was measured during the RIE of Al, using a non-contact thermometer (a fluorescence optical fiber thermometer), the following results were obtained. Where many substrates were simultaneously subjected to the etching treatment (in which the loading effect decreased the etching rate and rf power density), the substrate temperature became 100.degree. C. or more, and where the substrates are subjected to the etching treatment one by one, the substrate temperature became 130.degree. C. or more. Under these conditions the Al was etched in a vertical direction or in an inverse taper. Therefore, to realize a taper etching, a decrease of the selectivity of the Al over resist or the addition of a carbon-containing gas must be adopted, as explained hereinabove.
According to the principle of fluorescence optical fiber thermometry, a small amount of phosphor is coated on the back of the substrate, an excitation light is applied to the phosphor through an optical fiber, fluorescence of the phosphor is observed through the fiber, and the fluorescent decay time is measured to determine the substrate temperature. In this way, the temperature can be easily measured without the problem of disturbance of the process.